An incandescent lamp having a carbide-containing luminous element is known from many documents. An as yet unsolved problem is the brittleness of such a luminous element, something which greatly limits the service life. It is true that a possibility mentioned in U.S. Pat. No. 3,405,328 consists in dissolving the carbon in excess in the tantalum carbide luminous element. The carbon evaporated to the outside by the luminous element and which is deposited on the bulb wall is then replaced by diffusion from the interior outward.
A further possibility constitutes the addition of carbon and hydrogen to the filling gas, see U.S. Pat. No. 2,596,469, for example. A cyclic carbon process arises in this case in the lamp. The carbon evaporated at high temperatures reacts at lower temperatures with hydrogen to produce hydrocarbons which, through convection and/or diffusion, are transported back to the filament where they decompose again. The carbon produced in the process is adsorbed again onto the filament. It is mostly necessary to use a hydrogen excess for a functioning cyclic carbon process, in order to avoid the deposition of carbon (in the form of carbon black) in the lamp vessel. The filament made from carbide which is used here is fastened on supply leads by crimping, for example.
In order to reduce the efficiency loss, in addition to hydrogen use has also been made of halogens for reaction with the carbon, see U.S. Pat. No. 3,022,438, for example. Here, the luminous element is fastened similarly on a frame. The carbon evaporated by the luminous element reacts in the cold regions near the bulb wall with, for example, chlorine atoms to form compounds such as CCl4, deposition of the carbon on the wall thereby being avoided. The carbon/halogen compounds are transported back in the direction of the incandescent element by transport processes such as convention and diffusion, decomposing in the warmer region and releasing the carbon in the process. The carbon can be adsorbed again onto the filament.